Catechol-O-methyltransferase in complex with substituted 3'-deoxyribose bisubstrate inhibitors.

The biological activity of catechol neurotransmitters such as dopamine in the synapse is modulated by transporters and enzymes. Catechol-O-methyltransferase (COMT; EC 2.1.1.6) inactivates neurotransmitters by catalyzing the transfer of a methyl group from S-adenosylmethionine to catechols in the presence of Mg²âº. This pathway also inactivates L-DOPA, the standard therapeutic for Parkinson's disease. Depletion of catechol neurotransmitters in the prefrontal cortex has been linked to schizophrenia. The inhibition of COMT therefore promises improvements in the treatment of these diseases. The concept of bisubstrate inhibitors for COMT has been described previously. Here, ribose-modified bisubstrate inhibitors were studied. Three high-resolution crystal structures of COMT in complex with novel ribose-modified bisubstrate inhibitors confirmed the predicted binding mode but displayed subtle alterations at the ribose-binding site. The high affinity of the inhibitors can be convincingly rationalized from the structures, which document the possibility of removing and/or replacing the ribose 3'-hydroxyl group and provide a framework for further inhibitor design.

The dynamics of Aß distribution after γ-secretase inhibitor treatment, as determined by experimental and modelling approaches in a wild type rat.

Inhibition of the enzyme(s) that produce the Amyloid beta (Aß) peptide, namely BACE and γ-secretase, is considered an attractive target for Alzheimer's disease therapy. However, the optimal pharmacokinetic-pharmacodynamic modelling method to describe the changes in Aß levels after drug treatment is unclear. In this study, turnover models were employed to describe Aß levels following treatment with the γ-secretase inhibitor RO5036450, in the wild type rat. Initially, Aß level changes in the brain, cerebral spinal fluid (CSF) and plasma were modeled as separate biological compartments, which allowed the estimation of a compound IC50 and Aß turnover. While the data were well described, the model did not take into consideration that the CSF pool of Aß most likely originates from the brain via the CSF drainage pathway. Therefore, a separate model was carried out, with the assumption that CSF Aß levels originated from the brain. The optimal model that described the data involved two brain Aß 40 sub-compartments, one with a rapid turnover, from which CSF Aß 40 is derived, and a second quasi-static pool of ~20%. Importantly, the estimated in vivo brain IC50 was in a good range of the in vitro IC50 (ratio, 1.4). In conclusion, the PK/PD models presented here are well suited for describing the temporal changes in Aß levels that occur after treatment with an Aß lowering drug, and identifying physiological parameters.

Molecular recognition at the active site of catechol-O-methyltransferase (COMT): adenine replacements in bisubstrate inhibitors.

L-Dopa, the standard therapeutic for Parkinson's disease, is inactivated by the enzyme catechol-O-methyltransferase (COMT). COMT catalyzes the transfer of an activated methyl group from S-adenosylmethionine (SAM) to its catechol substrates, such as L-dopa, in the presence of magnesium ions. The molecular recognition properties of the SAM-binding site of COMT have been investigated only sparsely. Here, we explore this site by structural alterations of the adenine moiety of bisubstrate inhibitors. The molecular recognition of adenine is of special interest due to the great abundance and importance of this nucleobase in biological systems. Novel bisubstrate inhibitors with adenine replacements were developed by structure-based design and synthesized using a nucleosidation protocol introduced by Vorbrüggen and co-workers. Key interactions of the adenine moiety with COMT were measured with a radiochemical assay. Several bisubstrate inhibitors, most notably the adenine replacements thiopyridine, purine, N-methyladenine, and 6-methylpurine, displayed nanomolar IC(50) values (median inhibitory concentration) for COMT down to 6 nM. A series of six cocrystal structures of the bisubstrate inhibitors in ternary complexes with COMT and Mg(2+) confirm our predicted binding mode of the adenine replacements. The cocrystal structure of an inhibitor bearing no nucleobase can be regarded as an intermediate along the reaction coordinate of bisubstrate inhibitor binding to COMT. Our studies show that solvation varies with the type of adenine replacement, whereas among the adenine derivatives, the nitrogen atom at position 1 is essential for high affinity, while the exocyclic amino group is most efficiently substituted by a methyl group.

Stepwise Design of γ-Secretase Modulators with an Advanced Profile by Judicious Coordinated Structural Replacements and an Unconventional Phenyl Ring Bioisostere.

Starting from RO6800020 (1), our former γ-secretase modulator (GSM) lead compound, we utilized sequential structural replacements to improve the potency (IC50), pharmacokinetic properties including the free fraction (fraction unbound (fu)) in plasma, and in vivo efficacy. Importantly, we used novel CF3-alkoxy groups as bioisosteric replacements of a fluorinated phenyl ring and properties such as lipophilicity, solubility, metabolic stability, and free fraction could be balanced, maintaining low Pgp efflux needed for CNS penetration. In addition, by reducing aromaticity, we prevented phototoxicity. Additional substitution in the triazolopyridine core disturbed the binding to phosphatidylinositol 4-kinase, catalytic ß (PIK4CB). We also introduced less lipophilic head heterocycles devoid of covalent binding (CVB) liability. After these changes, further modifications to the trifluoroethoxy bioisosteric replacement allowed rebalancing of properties, such as lipophilicity, and also potency. Our optimization strategy culminated with in vivo active RO7101556 (18B) having excellent properties and being selected as an advanced candidate.

Discovery of RO7185876, a Highly Potent γ-Secretase Modulator (GSM) as a Potential Treatment for Alzheimer's Disease.

γ-Secretase (GS) is a key target for the potential treatment of Alzheimer's disease. While inhibiting GS led to serious side effects, its modulation holds a lot of potential to deliver a safe treatment. Herein, we report the discovery of a potent and selective gamma secretase modulator (GSM) (S)-3 (RO7185876), belonging to a novel chemical class, the triazolo-azepines. This compound demonstrates an excellent in vitro and in vivo DMPK profile. Furthermore, based on its in vivo efficacy in a pharmacodynamic mouse model and the outcome of the dose range finding (DRF) toxicological studies in two species, this compound was selected to undergo entry in human enabling studies (e.g., GLP toxicology and scale up activities).

Discovery of Balovaptan, a Vasopressin 1a Receptor Antagonist for the Treatment of Autism Spectrum Disorder.

We recently reported the discovery of a potent, selective, and brain-penetrant V1a receptor antagonist, which was not suitable for full development. Nevertheless, this compound was found to improve surrogates of social behavior in adults with autism spectrum disorder in an exploratory proof-of-mechanism study. Here we describe scaffold hopping that gave rise to triazolobenzodiazepines with improved pharmacokinetic properties. The key to balancing potency and selectivity while minimizing P-gp mediated efflux was fine-tuning of hydrogen bond acceptor basicity. Ascertaining a V1a antagonist specific brain activity pattern by pharmacological magnetic resonance imaging in the rat played a seminal role in guiding optimization efforts, culminating in the discovery of balovaptan (RG7314, RO5285119) 1. In a 12-week clinical phase 2 study in adults with autism spectrum disorder balovaptan demonstrated improvements in Vineland-II Adaptive Behavior Scales, a secondary end point comprising communication, socialization, and daily living skills. Balovaptan entered phase 3 clinical development in August 2018.

Alzheimer's disease: from pathology to therapeutic approaches.

Mind how you go: The current strategies for the development of therapies for Alzheimer's disease are very diverse. Particular attention is given to the search for inhibitors (see picture for two examples) of the proteolytic enzyme beta- and gamma-secretase, which inhibits the cleavage of the amyloid precursor proteins into amyloid beta peptides, from which the disease-defining deposits of plaque in the brains of Alzheimer's patients originates.Research on senile dementia and Alzheimer's disease covers an extremely broad range of scientific activities. At the recent international meeting of the Alzheimer's Association (ICAD 2008, Chicago) more than 2200 individual scientific contributions were presented. The aim of this Review is to give an overview of the field and to outline its main areas, starting from behavioral abnormalities and visible pathological findings and then focusing on the molecular details of the pathology. The "amyloid hypothesis" of Alzheimer's disease is given particular attention, since the majority of the ongoing therapeutic approaches are based on its theoretical framework.

Substituted 2-oxo-azepane derivatives are potent, orally active gamma-secretase inhibitors.

A hydroxamic acid screening hit 1 was elaborated to 5,5-dimethyl-2-oxoazepane derivatives exhibiting low nanomolar inhibition of gamma-secretase, a key proteolytic enzyme involved in Alzheimer's disease. Early ADME data showed a high metabolic clearance for the geminal dimethyl analogs which could be overcome by replacement with the bioisosteric geminal difluoro group. Synthesis and structure-activity relationship are discussed and in vivo active compounds are presented.

Design of Potent and Druglike Nonphenolic Inhibitors for Catechol O-Methyltransferase Derived from a Fragment Screening Approach Targeting the S-Adenosyl-l-methionine Pocket.

A fragment screening approach designed to target specifically the S-adenosyl-l-methionine pocket of catechol O-methyl transferase allowed the identification of structurally related fragments of high ligand efficiency and with activity on the described orthogonal assays. By use of a reliable enzymatic assay together with X-ray crystallography as guidance, a series of fragment modifications revealed an SAR and, after several expansions, potent lead compounds could be obtained. For the first time nonphenolic and small low nanomolar potent, SAM competitive COMT inhibitors are reported. These compounds represent a novel series of potent COMT inhibitors that might be further optimized to new drugs useful for the treatment of Parkinson's disease, as adjuncts in levodopa based therapy, or for the treatment of schizophrenia.

Generation of vascular endothelial and smooth muscle cells from human pluripotent stem cells.

The use of human pluripotent stem cells for in vitro disease modelling and clinical applications requires protocols that convert these cells into relevant adult cell types. Here, we report the rapid and efficient differentiation of human pluripotent stem cells into vascular endothelial and smooth muscle cells. We found that GSK3 inhibition and BMP4 treatment rapidly committed pluripotent cells to a mesodermal fate and subsequent exposure to VEGF-A or PDGF-BB resulted in the differentiation of either endothelial or vascular smooth muscle cells, respectively. Both protocols produced mature cells with efficiencies exceeding 80% within six days. On purification to 99% via surface markers, endothelial cells maintained their identity, as assessed by marker gene expression, and showed relevant in vitro and in vivo functionality. Global transcriptional and metabolomic analyses confirmed that the cells closely resembled their in vivo counterparts. Our results suggest that these cells could be used to faithfully model human disease.

X-ray Crystal Structure of a Bisubstrate Inhibitor Bound to the Enzyme Catechol-O-methyltransferase: A Dramatic Effect of Inhibitor Preorganization on Binding Affinity.

With an IC50 value of 9 nM, 1 is the most potent known disubstrate inhibitor for catechol-O-methyltransferase (COMT). Inhibition of COMT is of significant interest in the therapy of Parkinsonapos;s disease since it ensures that a larger percentage of orally administered L-dopa reaches-in the form of dopamine-its target in the brain. The X-ray crystal structure of a complex formed by COMT and 1 has been solved at 2.6-Å resolution.

Bisubstrate inhibitors of catechol O-methyltransferase (COMT): the crucial role of the ribose structural unit for inhibitor binding affinity.

Inhibition of the enzyme catechol O-methyltransferase offers a therapeutic handle to regulate the catabolism of catecholamine neurotransmitters, providing valuable assistance in the treatment of CNS disorders such as Parkinson's disease. A series of ribose-modified bisubstrate inhibitors of COMT featuring 2'-deoxy-, 3'-deoxy-, 2'-aminodeoxy-3'-deoxy-, and 2'-deoxy-3'-aminodeoxyribose-derived central moieties and analogues containing the carbocyclic skeleton of the natural product aristeromycin were synthesized and evaluated to investigate the molecular recognition properties of the ribose binding site in the enzyme. Key synthetic intermediates in the ribose-derived series were obtained by deoxygenative [1,2]-hydride shift rearrangement of adenosine derivatives; highlights in the synthesis of carbocyclic aristeromycin analogues include a diastereoselective cyclopropanation step and nucleobase introduction with a modified Mitsunobu protocol. In vitro biological evaluation and kinetic studies revealed dramatic effects of the ribose modification on binding affinity: 3'-deoxygenation of the ribose gave potent inhibitors (IC50 values in the nanomolar range), which stands in sharp contrast to the remarkable decrease in potency observed for 2'-deoxy derivatives (IC50 values in the micromolar range). Aminodeoxy analogues were only weakly active, whereas the change of the tetrahydrofuran skeleton to a carbocycle unexpectedly led to a complete loss of biological activity. These results confirm that the ribose structural unit of the bisubstrate inhibitors of COMT is a key element of molecular recognition and that modifications thereof are delicate and may lead to surprises.

Bisubstrate inhibitors for the enzyme catechol-O-methyltransferase (COMT): influence of inhibitor preorganisation and linker length between the two substrate moieties on binding affinity.

Inhibition of the enzyme catechol-O-methyltransferase (COMT) is an important approach in the treatment of Parkinson's disease. A series of new potent bisubstrate inhibitors for COMT, resulting from X-ray structure-based design and featuring adenosine and catechol moieties have been synthesised. Biological results show a large dependence of binding affinity on inhibitor preorganisation and the length of the linker between nucleoside and catechol moieties. The most potent bisubstrate inhibitor for COMT has an IC50 value of 9 nM. It exhibits competitive kinetics for the SAM and mixed inhibition kinetics for the catechol binding site. Its bisubstrate binding mode was confirmed by X-ray structure analysis of the ternary complex formed by the inhibitor, COMT and a Mg2+ ion.

Influenza virus infection is not affected by serum amyloid P component.

BACKGROUND: Binding of serum amyloid P component (SAP) to its ligands, including bacteria, chromatin and amyloid fibrils, protects them from degradation, is anti-opsonic and anti-immunogenic. SAP thereby enhances the virulence of pathogenic bacteria to which it binds. However SAP also contributes to host resistance against bacteria to which it does not bind. Human SAP has been reported to bind to the influenza virus and inhibit viral invasion of cells in tissue culture. We therefore investigated a possible role of SAP in either host resistance or viral virulence during influenza infection in vivo. MATERIALS AND METHODS: The clinical course of mouse adapted influenza virus infection, the host antibody response, and viral replication, were compared in wild type mice, mice with targeted deletion of the SAP gene, and mice transgenic for human SAP. The effects of reconstitution of SAP deficient mice with pure human SAP, and of a drug that specifically blocks SAP binding in vivo, were also studied. Binding of mouse and human SAP to immobilized influenza virus was compared. RESULTS: The presence, absence, or availability for binding of SAP in vivo had no significant or consistent effect on the course or outcome of influenza infection, or on either viral replication or the anti-viral antibody response. Mouse SAP bound much less avidly than human SAP to influenza virus. CONCLUSIONS: In marked contrast to the dramatic effects of SAP deficiency on host resistance to different bacterial infections, mouse SAP apparently plays no significant role during infection of mice with influenza virus. Human SAP binds much more avidly than mouse SAP to the virus, but also had no effect on any of the parameters measured and is therefore unlikely to be involved in human influenza infection.